1. Field of the Invention
The present invention relates to a press device and method of using the same for treating a fibrous material web, and more specifically to a press device with variably adjustable pressure and line force.
2. Discussion of Background Information
The present invention relates to press device and method of using the same for treating a fibrous material web, in particular a paper and/or cardboard web. A press device has a press nip that is elongated in the web travel direction, and is formed between a shoe press unit and a counter roll. The press device also has a roll nip that is formed between the counter roll and another roll. The shoe press unit includes a flexible press belt, which revolves around a non-rotating carrier and, in the region of the elongated press nip, is supported on the carrier by at least one support element. The counter roll is embodied as a deflection compensation roll with a roll jacket, which revolves around a non-rotating carrier and; in the region of the elongated press nip, is in turn supported on the relevant carrier by at least one support element. Preferably the pressure fluid-actuated support elements are designed, and can be actuated, in such a way that a pressure differential is produced with regard to the internal pressures, which are generated by means of the support elements, and act on the flexible press belt of the shoe press unit or act on the roll jacket of the counter roll.
With a press device of this kind in which the shoe press is usually disposed on top, a line force that is as even as possible should be generated even in the roll nip that is not deflection-controlled, which is achieved by means of a corresponding pressure differential or a corresponding line force differential between the shoe press unit and the counter roll. The pressure differential brings about the fact that the line force acting in the elongated press nip formed between the shoe press unit and the counter roll is not compensated for to the full extent by means of the internal support elements of the counter roll. The remaining force causes a deformation of the counter roll both in the elongated press nip formed by the shoe press unit, which can be easily compensated for by the flexible support element of the shoe press unit, and in the roll nip formed between the counter roll and the other roll. If the pressure differential is selected, for example, so that a greater pressure occurs in the shoe press unit than in the counter roll, then a deflection of the counter roll occurs in form of a bulging towards the other roll in the roll nip formed between the counter roll and the other roll. Due to this bulging, the counter roll and the other roll can, for example, be embodied with a reduced cambering for the deflection compensation. With a slighter cambering of this kind, the speed differentials between the roll center and the roll ends can be kept small. In particular, such a line force differential can consequently be produced between the shoe press unit and the counter roll, which produces a deflection of the counter roll in the roll nip and as a result, permits a reduction of the required cambering in this roll nip.
DE-A-195 20 443.3 discloses a press device where the pressure differential or the line force differential is fixed at a constant value. However, a fixed pressure differential, just as the lack of a pressure differential, brings with it the disadvantage that the line force can only be adjusted, at most, in a very limited range. This can in particular be traced to the fact that the deformations, that are a function of the line force, can no longer be correctly compensated for by means of the fixed camberings provided and this consequently leads to deviations of the pressure profile occurring over the web width.
It is also known to have a central roll that has an additional series of support elements which are provided in the direction of the roll nip toward the preceding roll, and regulates the deflection compensation in this roll nip. However, this presents a problem in that such an additional series of support elements is connected with considerable additional expenditures, and is correspondingly costly.